These disconnectors, commonly called switches, fuses-switches or change-over switches are designed to distribute energy to electrical installations or to control alternating low voltage industrial equipment, for example 380 V, and in a current range from a few dozen to a few thousand amps. So-called double disconnectors comprise two moving contacts per pole or disconnecting module. More often than not, the moving contacts are made up of a rectilinear bar which performs a perfect translation movement between its two stable positions and the fixed contacts of a same pair are arranged in the same plane parallel to said moving contact. The translation movement of the moving contacts is traditionally obtained by a cam securely fixed at its center to the disconnecting modules control shaft. The cam may have an almost oval shape and comprise a guide path on its section. In this case, each moving contact is connected to a moving element provided on either side of the control shaft and applied against the section of the oval cam by means of a spring. The rotation of the cam generated by the rotation of the control shaft drives the moving element in a radial translation movement transmitted simultaneously to the corresponding moving contact. The virtually oval shape of the cam is generally optimized to allow a sudden disconnection and an optimum operating force. The cam can also be round on which the moving elements are fixed at out-of-center points, thereby forming a rod-wheel system. In this way, the rotation of the cam also drives the radial translation of the moving element which is transmitted to the corresponding moving contact.
The known disconnectors described briefly above present numerous drawbacks. Due to the fact that the moving contacts perform a perfect translation movement, there is no friction between the moving contacts and the fixed contacts when engaging and releasing takes place. Consequently, there is no self cleaning of the contact surfaces. This is detrimental to the quality of the electrical contact. In particular, the contact resistance increases with the number of operations performed and the number of electric arcs established between the fixed and moving contacts. The deterioration in the quality of electrical contact causes the contact surfaces and the device in general to heat up, leading to Joule effect losses, as well as a reduction in the lifetime of both the contacts and the device. Furthermore, in the standard devices, there is a relatively large number of parts. In particular, several intermediate current-carrying parts have to be arranged to achieve the complete circuit from the input terminal to the output terminal. As these parts are frequently made of copper, the cost price of the disconnecting modules remains relatively high. Furthermore, the force applied to the moving contact corresponds to that applied by the cam securely fixed to the control shaft which is itself securely fixed to the operating handle. However, due to the fact that each rectilinear moving contact co-operates with two fixed contacts arranged in the same plane, the force applied on each fixed contact corresponds to half the force transmitted by the cam. This implies increasing the operating force on the handle to increase the force on the contacts, which is contrary to the objective being sought when engaging. What is more, in standard disconnecting devices, the speed and the distance the moving contacts move according to the time are identical when engaging and releasing, which is detrimental to optimizing the physical conditions in either of the stable positions. Indeed, when engaging, the smallest possible operating force is sought, as well as the quickest possible engaging speed. On the other hand, when releasing, a sudden disconnection is sought to avoid electric arcs occurring as much as possible, as well as good resistance to a force equal to three times the operating force, commonly called 3F and defined by an international standard.
Some publications describe electrical disconnecting devices designed to create friction between the fixed and moving contacts when engaging takes place. This is notably the case in publications EP-A-252 285, EP-A-105 817 and CH-A-352 024. Nevertheless, none of them provides for a special layout of the contacts making it possible to increase the contact force between them, nor different trajectories of the moving contacts for the engaging and the releasing operations in order to optimize the operating conditions.
In publication EP-A-252 285, it is a matter of a circuit breaker limited to low currents (under 32 A) for domestic applications, which is provided with a single disconnecting module and not an industrial switch provided with several disconnecting modules. What is more, the contact surfaces provided on the fixed contact and the moving contact are coplanar. It is the mechanism for transmitting movement between the circuit breaker's lever and the moving contact which generates a friction movement between the two contacts.
In publication EP-A-105 817, it is a question of a multistage switch limited to currents from 25 to 32 A whose cam mechanism is only designed to ensure self-cleaning of the contacts by means of an auxiliary cam which controls a carriage which moves the moving contacts by friction on the fixed contacts. The contact surfaces provided on these fixed and moving contacts are also coplanar.
In publication CH-A-352 024, it is a matter of a switch with two moving contacts, whose contact surfaces are also coplanar, controlled by a central rotating cam. The approach movement of the moving contacts is performed according to an angle of 20 to 30.degree. which, when contact is made, leads to a pressure and self-cleaning friction on the contacts.